I. Field of the Invention
This invention relates to starches which are crosslinked with sodium trimetaphosphate and to foodstuffs thickened therewith. More particularly it provides a dual derivatizing process which unexpectedly leads to crosslinked starches which provide superior viscosity characteristics when used as thickeners as compared to crosslinked starches of the prior art.
II. Brief Description of the Prior Art
Recent attempts to replace certain starch derivatives used in foods, e.g. epichlorohydrin inhibited starches, with other FDA acceptable starch derivatives, have placed new emphasis on starch derivatives formed with phosphate derivatizing reagents, especially sodium trimetaphosphate.
Methods for the production of starch phosphate esters have long been known. Thus U.S. Pat. Nos. 2,884,413, 2,801,242, 2,852,393 and 3,021,222, among others are directed to processes for the production of such starch derivatives and the various uses thereof. These derivatives, when contrasted with the corresponding raw, unmodified starches, will differ in properties depending upon the base starch employed. In the case of corn starch, the crosslinked starch gelatinizes somewhat earlier than the raw starch, reaches a higher peak or maximum viscosity and breaks down to a lesser extent than the raw starch. In the case of crosslinked amioca starch there is also less breakdown than the raw amioca with the crosslinked starch products maintaining their maximum viscosity under prolonged agitation, elevated temperature and low pH. Additionally, there is an improvement in the textural properties of the crosslinked starches when contrasted with the unmodified starch. Despite these advantages over the unmodified starches, when the crosslinked starches are re-slurried, drum dried and ground to a fine powder to make a starch useful in cold water swelling applications, serious deficiencies can be noted. Thus after the viscosity peak is achieved and maintained for a period of time in the initial dispersion, there is a loss of viscosity or "breakdown" in many food systems after subsequent cooking or baking. This breakdown results in a loss of both useable thickening power and textural properties, with a high breakdown usually indicating a gummy, cohesive texture and reversion of the starch to its original unmodified characteristics. Another such disadvantage is evidenced in thinning of starch stabilized fruit pastes in certain bakery products such as fruit filled tarts. This thinning often results in a "boil-out" or puncture of the pastry shell during baking thereby detracting from the appearance of the tart.